If I understand correctly what an averate rate of change is, I'd say it's :
I think the answer is 2 if you are getting the average of the function and it is zero if you are getting the average of its derivative(rate).
The averaging of a function involves the integration of the function between the limits given divided by the interval. Of course you sould substitute the limits in radians.
This is purely mathematical.
if you graph this function you will find it a sine wave shifted upwards two units. so the average is two without computing.